Effect of process parameters on the synthesis of mesoporous nanocrystalline zirconia with triblock copolymer as template

Nanocrystalline zirconia powders with high surface area, mesoporous structure and tetragonal crystallite phase have been prepared by the surfactant-assisted route by using of Pluronic P123 block copolymer surfactant. The effect of several process parameters such as the type of zirconium precursor, pH value, refluxing time, refluxing temperature and surfactant to zirconium molar ratio on the structural properties of the powders have been investigated.     

Improved photocatalytic oxidation of ciprofloxacin by NiS-coupled WO3 nanorods synthesized by solvothermal method under visible light

Photocatalytic oxidation of antibiotics over semiconducting nanostructured photocatalysts is stared as a capable procedure for preventing possible antimicrobial resistance. Accordingly, plenteous research suggestions for photocatalyst design and trials are investigated to realize this approach. Moreover, photostability and reusability are important factors for sustainable utilization. Herein, tungsten trioxide (WO₃) nanorods were grown by a solvothermal route in the presence of double soft templates, followed by incorporating nickel sulfide (NiS) nanoparticles on their surface to have NiS/WO₃ nanocomposite photocatalysts. These formed heterojunctions were analyzed via several tools. The NiS incorporation has widened the visible-light harvesting owing to the bandgap reduction from 2.82 eV for pure WO₃ to 2.40 eV at 9 wt% of NiS. The mesoporous surface has not been meaningfully impacted by incorporating NiS with a value of the surface area between 163 and 189 m² g^-1. The photooxidation of ciprofloxacin (CiP) over the formed photocatalysts were done under visible-light irradiation. The 2.0 g L^-1 of 9% NiS/WO₃ has completely oxidized 30.2 μmol CiP at a 1.38 μmol min⁻¹. This progressive NiS/WO₃ p-n heterojunction has also implied reusability for five repetitive cycles. This excellent photoactivity is ascribed to the charge transfer by the S-scheme mechanism and the synergistic upshot of a particular NiS expanse.     

Preparation of copper-containing mesoporous manganese oxides and their catalytic performance for CO oxidation

Copper-containing mesoporous manganese oxides were prepared by the sol–gel method. The samples obtained were characterized by XRD, N₂ adsorption–desorption, ICP, CO-TPD, redox measurement and XPS. After calcination at 300 °C, amorphous structure was shown by XRD for all the samples. All the samples had mesopores of about 6 nm and high surface areas of 170–230 m² g⁻¹. Using these samples as catalysts, CO oxidation was carried out as a model reaction. Copper-containing mesoporous manganese oxide prepared by the sol–gel method showed a very high activity. On the other hand, copper-supported manganese oxide prepared by the impregnation method using copper sulfate showed a low activity. Differences in activities were correlated with the mobility of lattice oxygen.     

Promotional effect of gold added to palladium supported on a new mesoporous TiO2 for total oxidation of volatile organic compounds

Gold and palladium were supported on a mesoporous TiO₂ for total oxidation of volatile organic compounds (VOCs). Mesoporous high surface area titania support was synthesised using of Ti(OC₂H₅)₂ in the presence of CTMABr surfactant. After removing the surfactant molecules, 0.5 or 1.5 wt% of palladium and 1 wt% of gold were precipitated on the support by, respectively, wet impregnation and deposition–precipitation methods. The activity for toluene and propene total oxidation of the prereduced samples follows the same order: 0.5%Pd-1%Au/TiO₂ > 1.5%Pd/TiO₂ > 0.5%Pd/TiO₂ > 1%Au-0.5%Pd/TiO₂ > 1%Au/TiO₂ > TiO₂. Moreover, a catalytic comparison with samples based on a conventional TiO₂, shows the catalytic advantage of the mesoporous TiO₂ support. The promotional effect of gold added to palladium could be partly explained by small metallic particles (TEM), but meanly by metallic particles made up of Au-rich core with a Pd-rich shell. Moreover, the hydrogen TPR profile of 0.5%Pd-1%Au/TiO₂ shows only the signal attributed to small PdO particles. Gold also implies a protecting effect of the support under reduction atmosphere. Operando diffuse reflectance infrared fourier transform (DRIFT) spectroscopy was carried on and allowed to follow the VOCs oxidation and the formation of coke molecules, but also a metallic electrodonor effect to the adsorbed molecule which increases in the same order as the activity for oxidation reaction. The presence of coke after test was also shown by DTA–TGA by exothermic signals between 300 and 500 °C and by EPR (g = 2.003).     

Optimization, Yield Studies and Morphology of WO3 Nano-Wires Synthesized by Laser Pyrolysis in C2H2 and O2 Ambients—Validation of a New Growth Mechanism

Laser pyrolysis has been used to synthesize WO₃ nanostructures. Spherical nano-particles were obtained when acetylene was used to carry the precursor droplet, whereas thin films were obtained at high flow-rates of oxygen carrier gas. In both environments WO₃ nano-wires appear only after thermal annealing of the as-deposited powders and films. Samples produced under oxygen carrier gas in the laser pyrolysis system gave a higher yield of WO₃ nano-wires after annealing than the samples which were run under acetylene carrier gas. Alongside the targeted nano-wires, the acetylene-ran samples showed trace amounts of multi-walled carbon nano-tubes; such carbon nano-tubes are not seen in the oxygen-processed WO₃ nano-wires. The solid–vapour–solid (SVS) mechanism [B. Mwakikunga et al., J. Nanosci. Nanotechnol., 2008] was found to be the possible mechanism that explains the manner of growth of the nano-wires. This model, based on the theory from basic statistical mechanics has herein been validated by length-diameter data for the produced WO₃ nano-wires.     

Sonochemical synthesis of tungsten carbide-palladium nanocomposites and their electrocatalytic activity for hydrogen oxidation reaction

Nanocomposites between β-WC and Pd nanoparticles supported on carbon are synthesized and their electrocatalytic properties for the hydrogen oxidation reaction have been investigated. The Pd nanoparticles are obtained by a chemical reduction reaction of PdCl₂ and the β-WC nanoparticles by a sonochemical decomposition of W(CO)₆ on Pd-loaded carbon followed by heat-treatment. Depending on the relative amounts of W to Pd, the Pd nanoparticles can be reacted with W to form Pd-W alloy nanoparticles. The Pd-W alloy, whose composition is estimated to have W less than 18 at.% based on its lattice parameter, lost most of the catalytic activity of Pd. On the other hand, the nanocomposite between β-WC and pure Pd shows an enhanced activity compared with that of Pd nanoparticles alone. This enhancement can be explained with the H⁺-spill-over to β-WC.     

Preparation of mesoporous In–Nb mixed oxides and its application in photocatalytic water splitting for hydrogen production

A series of mesoporous In–Nb mixed oxides was synthesized using NbCl₅ and In₂O₃ as the starting material and triblock copolymer P123 as template. We investigated the influence of indium content on the synthesis and characteristics of the mesoporous In–Nb mixed oxides, and their photocatalytic activities for water splitting. The materials were characterized by small angle X-ray scattering, powder X-ray diffraction, extended X-ray absorption fine structure, transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometer, N₂ sorption and UV–vis spectroscopy. The surface area of mesoporous In–Nb mixed oxides was greater than 90 m²/g with a wormhole framework. The optimization of synthesis condition of the mesoporus In–Nb oxides catalyst contained a small fraction of highly dispersed indium (In/Nb = 0.13) species intercalated into the framework of mesoporous niobium oxides and exhibited a high photocatalytic activity for water splitting reaction which was about 2.7 times as compared to mesoporous Nb₂O₅ and was about 19 times higher than commercial bulk Nb₂O₅.     

以水玻璃为硅源喷雾干燥制备SiC前驱体

以廉价的水玻璃和炭黑为原料,通过制备均匀混合的前驱体,利用碳热还原反应合成出超细SiC粉体。比较研究了前驱体喷雾干燥与搅拌干燥两种制备方法对体系碳热还原反应的影响,重点考察了喷雾干燥制备过程中主要工艺参数对前驱粉体密度及收率的影响。结果表明:喷雾制备的前驱体具有更高的反应活性,在1550℃下反应2h就可使SiO2转化率达到89.4%,搅拌干燥制备的前驱体转化率只有65.2%。喷雾干燥过程中,适当提高进口温度、喷雾头转速并降低料液的固体含量,可获得高收率、高产率的前驱粉体,利于整个制备工艺生产效率及产率的提高。     

Tunable emission and applications of Ln3+ doped NaGd(WO4)2 nanocrystals via a facile solvothermal process

Double tungstate crystal has outstanding capabilities of gain media for the application in mode-locked ultrafast lasers. Among them, NaGd(WO₄)₂:Ln³⁺ is widely using in laser, pH sensing or lighting devices. However, general synthetic methods require high temperature, long reaction time or adjustment of solution pH, which is seriously hinder their related applications. Here, we synthesized NaGd(WO₄)₂:Ln³⁺ nanocrystals through a solvothermal strategy. The synthesis was designed to avoid the solvent effect of water. Our nanoparticles with a rod shape and average size is ∼3.8 × 46.3 nm. Furthermore, Terbium and Europium ions co-doped in a single NaGd(WO₄)₂ host has been obtained, energy migration from Terbium ions to Europium ions also implemented. A series of emission colours (from green to white) were obtained. At last, a distinguished performance NaGd(WO₄)₂:0.03Tb,0.03Eu based UV-LED equipment was realized. Their adjustable emissions, convenient preparation method and special morphology reveal that NaGd(WO₄)₂:Ln³⁺ is a potential candidate for solid-state lasers and UV-LEDs applications.     

Synthesis of macroporous ZrO2–Al2O3 mixed oxides with mesoporous walls, using polystyrene spheres as template

Macroporous ZrO₂–Al₂O₃ mixed oxides with mesoporous walls were synthesized. The three-dimensional interconnected macroporous structures, of inorganic zirconia–alumina mixed oxides containing different alumina compositions (25, 50, 100 wt%), were prepared by sol–gel method from inorganic precursors and using polystyrene microspheres with diameters of 685 and 1520 nm as templates. The final porous arrays with controllable pore size in the submicrometer range could be obtained by calcination of the organic template. The structural characteristics are discussed. The physicochemical characterization of the samples was carried out by N₂ physisorption (S_BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The shrinkage of pore diameter was approximately 35%, and the wall thickness of inorganic framework varied between 135 and 154 nm. The specific surface areas, of the samples, were between 123 and 287 m²/g, obtaining the largest surface area with the highest alumina contents and the smallest templates.     

Synthesis and characterization of mesoporous Ta2O5–TiO2 photocatalysts for water splitting

Two series of Ta₂O₅–TiO₂ photocatalysts (Ta:Ti = 4:1, 1:1 and 1:4) were prepared by sol–gel technique applying triblock copolymer of Pluronic P123 and were tested in platinized form (0.3 wt.%) in photodecomposition of water under ultraviolet and visible light (λ > 300 nm). It was found the mesoporous character of tantalum containing catalysts with relatively high surface area (100–130 m² g⁻¹) of these samples. However, higher concentration of TiO₂ in mixed oxides leads to the destruction of mesoporous character of synthesized photocatalysts. All samples were characterized with thermogravimetry, XRD, N₂ physisorption, DR-UV–vis and FTIR spectroscopy. The mixed oxides of Ta₂O₅–TiO₂ system showed much lower band-gap than pure Ta₂O₅ and relatively high activity in platinized state in photocatalytic hydrogen generation under visible. Doping of pure oxides and mixed systems with sulfur resulted in lowering of the band-gap values below 3 eV and much better activity in H₂ evolution reaction. Non-platinized photocatalysts showed activity in liquid phase cyclohexene photooxidation at 305 K.     

Quasicatalytic and catalytic selective oxidation of methane to methanol over solid materials: a review on the roles of water

ABSTRACT

To date, although no commercial process for the selective oxidation of methane has been realized, various novel processes with effective solid materials operated at low temperature have been proposed. It is found that the addition of water in any processes not only influences the activity, selectivity, and stability of the solid materials but also affects the extraction efficiency of methanol from the product. Herein, the published results on the roles of water in the methanol production via the quasicatalytic and catalytic selective methane oxidation process using various solid materials in gas and liquid phases at low temperatures are critically reviewed.     

Preparation of hierarchical mesoporous CaCO3 by a facile binary solvent approach as anticancer drug carrier for etoposide

To develop a nontoxic system for targeting therapy, a new highly ordered hierarchical mesoporous calcium carbonate nanospheres (CCNSs) as small drug carriers has been synthesized by a mild and facile binary solvent approach under the normal temperature and pressure. The hierarchical structure by multistage self-assembled strategy was confirmed by TEM and SEM, and a possible formation process was proposed. Due to the large fraction of voids inside the nanospheres which provides space for physical absorption, the CCNSs can stably encapsulate the anticancer drug etoposide with the drug loading efficiency as high as 39.7 wt.%, and etoposide-loaded CCNS (ECCNS) nanoparticles can dispersed well in the cell culture. Besides, the drug release behavior investigated at three different pH values showed that the release of etoposide from CCNSs was pH-sensitive. MTT assay showed that compared with free etoposide, ECCNSs exhibited a higher cell inhibition ratio against SGC-7901 cells and also decreased the toxicity of etoposide to HEK 293 T cells. The CLSM image showed that ECCNSs exhibited a high efficiency of intracellular delivery, especially in nuclear invasion. The apoptosis test revealed that etoposide entrapped in CCNSs could enhance the delivery efficiencies of drug to achieve an improved inhibition effect on cell growth. These results clearly implied that the CCNSs are a promising drug delivery system for etoposide in cancer therapy.     

Metal-organic framework as a host for synthesis of nanoscale Co3O4 as an active catalyst for CO oxidation

Co₃O₄ nanoparticles were prepared from cobalt nitrate that was accommodated in the pores of a metal-organic framework (MOF) ZIF-8 (Zn(MeIM)₂, MeIM = 2-methylimidazole) by using a simple liquid-phase method. The ZIF-8 host was removed by pyrolysis under air and subsequently washing with an NH₄Cl–NH₃·H₂O aqueous solution. Transmission electron microscopy (TEM) analysis shows that the obtained Co₃O₄ is composed of separate nanoparticles with a mean size of 18 nm. The Co₃O₄ nanoparticles exhibit excellent catalytic activity, cycling stability, and long-term stability in the low temperature CO oxidation.     

The synthesis and characterization of monodispersed chitosan-coated Fe3O4 nanoparticles via a facile one-step solvothermal process for adsorption of bovine serum albumin

Preparation of magnetic nanoparticles coated with chitosan (CS-coated Fe₃O₄ NPs) in one step by the solvothermal method in the presence of different amounts of added chitosan is reported here. The magnetic property of the obtained magnetic composite nanoparticles was confirmed by X-ray diffraction (XRD) and magnetic measurements (VSM). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) allowed the identification of spherical nanoparticles with about 150 nm in average diameter. Characterization of the products by Fourier transform infrared spectroscopy (FTIR) demonstrated that CS-coated Fe₃O₄ NPs were obtained. Chitosan content in the obtained nanocomposites was estimated by thermogravimetric analysis (TGA). The adsorption properties of the CS-coated Fe₃O₄ NPs for bovine serum albumin (BSA) were investigated under different concentrations of BSA. Compared with naked Fe₃O₄ nanoparticles, the CS-coated Fe₃O₄ NPs showed a higher BSA adsorption capacity (96.5 mg/g) and a fast adsorption rate (45 min) in aqueous solutions. This work demonstrates that the prepared magnetic nanoparticles have promising applications in enzyme and protein immobilization.     

Functionalized sol–gels for mercury(II) separation: a comparison of mesoporous materials prepared with and without surfactant templates

Granular silica gels 1b (7.0 mol% ligand) and 1c (17.0 mol% ligand) containing different amounts of tethered mercapto ligand HS(CH₂)₃Si(O–)₃ were prepared in one step from the co-hydrolysis of HS(CH₂)₃Si(OMe)₃ and Si(OMe)₄. Analyses of 1b revealed that it was mesoporous (pore diameter: ca. 50 Å) with a large surface area (471 m²/g). In 0.5, 5.0, 50, and 500 ppm Hg²⁺ solutions, 1b was found to have Hg²⁺ uptake capacities comparable to those of sub-micron mesoporous powders prepared with two different surfactants in the current studies. 1b and 1c removed Hg²⁺ ions to be below 5 × 10⁻⁵ ppm (the detection limit of atomic absorption) from 0.368 and 50 ppm solutions, respectively. The granular 1b and 1c are easier to prepare and handle, and may offer an alternative to sub-micron powders prepared with surfactants for Hg(II) uptake.     

Development of mesoporous Bi2WO6/g-C3N4 heterojunctions via soft- and hard-template-assisted procedures for accelerated and reinforced photocatalytic reduction of mercuric cations under vis light irradiation

In this study, mesoporous Bi₂WO₆/g-C₃N₄ heterojunctions were developed using soft and hard templates [triblock copolymer surfactant (F127) and mesoporous silica (MCM-41), respectively]. The performance of the developed heterojunctions was assessed through the photocatalytic reduction of mercuric cations under Vis light illumination, with HCOOH being adopted to provide sacrificial holes agent. Surface measurements demonstrated that the fabricated specimens acquired large specific surface areas when compared with the neat ingredient. Furthermore, a transmission electron microscopy (TEM) analysis of the developed heterojunctions showed the homogeneous distribution of the spherical Bi₂WO₆ nanoparticles (NPs) on the surface of g-C₃N₄ nanosheets. Meanwhile, an accelerated rate (700 μ·mol·g^?1·h^?1) of photocatalytic mercuric cation reduction with improved efficiency (approximately 100%), compared with those of the pure ingredients [rate of 55 μ·mol·g^?1·h^?1 and efficiency of 13% for g-C₃N₄ nanosheets; rate of 95 μ·mol·g^?1·h^?1 and efficiency of 20% for mesoporous Bi₂WO₆ NPs], was accomplished via testing of the Bi₂WO₆/g-C₃N₄ heterojunction comprising 4 wt% Bi₂WO₆ after 40 min of illumination. Evidently, the efficiency of the photocatalytic reduction of mercuric cations endorsing the Bi₂WO₆/g-C₃N₄ heterojunction comprising 4 wt% Bi₂WO₆ NPs is 7.7 and 5 times more when compared with those of the neat g-C₃N₄ nanosheets and mesoporous Bi₂WO₆ NPs, respectively. The improved performance of the fabricated heterojunctions in the photocatalytic reduction of mercuric cations could be ascribed to i) fast diffusion of the mercuric cations through the mesoporous texture to the active ensembles, ii) greater specific surface area, iii) limited bandgap magnitude, iv) homogenous dispersion of the Bi₂WO₆ NPs on the surface of the nanosheets, and v) finite particle dimension of the mesoporous Bi₂WO₆ NPs. The durability and stability of the Bi₂WO₆/g-C₃N₄ heterojunctions were confirmed via their recyclability, which was maintained for up to five runs without pronounced activity loss.     

碳酸钠稳定过氧化物的环己烷氧化新技术研究

在1L高压反应釜内,以环己烷为原料,空气为氧源,碳酸钠为稳定剂,在158～164℃下进行环己烷空气氧化实验,考察了反应温度、稳定剂用量对环己烷氧化反应速度、转化率和选择性的影响以及稳定剂用量对环己基过氧化氢的稳定作用。结果表明:碳酸钠能很好的稳定环己基过氧化氢,提高了环己烷氧化反应的选择性,降低了反应速度。最佳的反应条件为反应温度160℃,反应压力1.0 MPa,碳酸钠加入量0.2 g,环己烷转化率在4%时,其选择性达92%以上。     

Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode

The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe²⁺ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe²⁺ and H₂O₂ electrogenerated at the O₂-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl⁻, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe³⁺-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated.     

A facile one-step synthesis and fabrication of hexagonal palladium-carbon nanocubes (H-Pd/C NCs) and their application as an efficient counter electrode for dye-sensitized solar cell (DSSC)

Hexagonal palladium-carbon nanocubes (H-Pd/C NCs) were prepared using a simple one-step chemical synthesis protocol and subsequently the prepared materials were used as the counter electrode (CE) in dye sensitized solar cell (DSSC) to replace the platinum (Pt) electrode. The H-Pd/C NCs were characterized by a variety of suitable analytical techniques including powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analysis to evaluate the crystalline, structural, morphological, compositional, chemical state and surface area. The BET nitrogen adsorption /desorption analysis shows that the as-prepared H-Pd/C NCs sample had a large surface area (568.8 m² g⁻¹) with average pore size of ∼3 nm. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses indicate that the H-Pd/C NCs have low charge-transfer resistance on the electrolyte/electrode interface and high electrocatalytic activity for the reduction of triiodide to iodide redox electrolyte and hence it is used as a CE in DSSC. The H-Pd/C NCs showed an overall power conversion efficiency (PCE) of 4.1% which performance is comparable with the conventional Pt CE (4.0%) under the identical condition.